In general, transceivers which may be applied for communication issues comprise a transmitter and a receiver that may operate simultaneously on different frequencies in FDD (Frequency Division Multiplex) systems, such as WCDMA (Wideband Code Division Multiple Access) or LTE (Long Term Evolution). Embodiments of the present invention relate particularly to transceivers for mobile wireless application.
In the forthcoming future, transmitters are expected to use a full-digital solution. In particular, in a transmitter based on a direct digital-to-RF conversion technique a conventional analog baseband filtering is not possible due to the missing analog baseband domain. In order to achieve a required floor noise at the own receiver Rx in an FDD system, the quantization noise needs to be attenuated into a lower level than in a conventional D/A converter by digital noise shaping.
However, digital noise shaping requires excess bandwidth, where the quantization noise can be processed. Such processing facilitates the more excess bandwidth is available.
A problem is that performing the noise shaping at a high rate with the full bit width of the transmitted signal is computationally expensive. That is, digital multiplier cost is largely proportional to the square of the bit width.
Further, simply noise shaping the whole signal before D/A conversion is not attractive, as it would require running the whole converter at a rather high sampling rate.
Hence, there is the need to avoid/reduce the problems mentioned above in transmitter noise shaping.
The following references may be relevant to the teachings herein:    “A Fully Digital 65 nm CMOS Transmitter for the 2.4-to-2.7 GHz WiFi/WiMAX Bands using 5.4 GHz ΔΣ RF DACs”; Pozsgay, Andreas; Solid-State Circuits Conference, 2008. ISSCC 2008. Digest of Technical Papers. IEEE International    “Oversampling Interpolating DACs”; Kester, Walt; ANALOG DEVICES MT-017 TUTORIAL    “Noise Shaping”; Nentwig, Markus; DSP blog at DSPrelated.com    P. Eloranta, P. Seppinen, “Direct-Digital RF-Modulator IC in 0.13 um CMOS for Wide-Band Multi-radio Applications”, in ISSCC Dig. Tech. papers, February 2005, pp. 532-615.